THE SOUTHWORTH PLANETARIUM 207-780-4249 www.usm.maine.edu/planet 70 Falmouth Street Portland, Maine 04103 43.6667° N, 70.2667° W Founded January 1970 "340 days until Christmas" THE DAILY ASTRONOMER Tuesday, January 19, 2016 Five Planets For the first time since 2005, all five naked eye planets,* will be visible simultaneously in the pre-dawn skies starting tomorrow! Those hearty sky watchers who are either impervious to or highly tolerant of the bitter cold can venture outside at 6:00 a.m. to see Jupiter, Mars, Saturn, Venus and Mercury. The first planet to rise, Jupiter, appears around 10:00 p.m. This behemoth world heralds the eventual appearance of the lesser planets. Mars follows around midnight. Though not as bright as Jupiter, the fourth planet's reddish color makes it distinct against the backdrop of white stars. Next comes Saturn: the most distant of the naked eye planets. Yellowish in appearance, Saturn is also dimmer than Jupiter and, in terms of color contrast, not as distinctive as Mars. However, like the other planets, it doesn't appear to twinkle, as the stars do. This twinkle, or scintillation, affects stars more than planets because the former is a pin point light source. The latter, being disc like, exudes a more concentrated light. Venus arrives next in the very early morning, when the sky is tinctured by the first hints of twilight. Venus is the brightest of the five and, therefore, the easiest to observe. Finally, Mercury emerges as the twilight brightens. Of the five naked eye planets, Mercury will be the most difficult to find. As it is the closest planet to the Sun, Mercury never appears to stray far from it. We'll have the opportunity to see all these planets for the next few weeks, at which point Mercury will dive below the eastern horizon. The best time to venture out is late January, when Mercury will be in a more favorable position. One will notice that the planets seem to describe an arc through the sky, as opposed to being scattered in all directions. This alignment is no coincidence. When forming, the solar system spread out like a disc. The planets formed from the peripheral gas surrounding the Sun and therefore are positioned along this disc. Earth travels along the same disc. In fact, Earth's orbital plane defines the "ecliptic," which we perceive as the Sun's apparent annual path through the heavens. The planets travel along a narrow band centered on this ecliptic because they are moving within the same disc in which the Sun revolves. Planet watchers rejoice! All five visible planets are up for viewing. *Mercury, Venus, Mars, Jupiter and Saturn are deemed the "naked eye planets" as they are observable with just the unaided eye. Of course, some astronomers claim that Uranus is also a naked eye planet when at its maximum brightness. While this statement is true, even at its brightest, Uranus only looks like a faint star.